Conventional circuits of this type include as a rule open loop systems. In other words, the signal from a sensor measuring the value is supplied to an analog-to-digital converter (A/D converter) without any feed back coupling or any feed back from the converter to the sensor circuit. This is evident, for example, from the article "Mikrovolt Messen" (Funkschau 14/1983, pp. 37/38) which describes and A/D converter, which operates in accordance with the principle of charge balancing (called hereinbelow ChB), and wherein there is supplied a signal, for example from a temperature sensor, to an input of the A/D converter. The ChB method is known, for example, from "Elektronik", vol. 12/1974, pp. 469-472, and from U.S. Pat. No. 3,790,886. Special temperature measuring circuits of this type are known from the German published application Nos. 3,129,476 and 3,130,499. Both also use an "open loop" system of a sensor measuring a value and an A/D converter. Moreover, in neither case is a pure resistance ratio measurement made. In one case the resistances of the switches, which connect the reference- or the measured resistance to the A/D converter, are included in the measurement (3,129,476). In the other case (3,130,499) the capacity of a capacitor is included in the measured value determination, and can affect the accuracy of the results.